1. Field of the Invention
The present invention relates to an optical symbol reading apparatus and a reading method.
2. Description of the Related Art
In recent years, steel instruments for medical purposes are often marked with optical symbols for such purposes as article management. The steel instruments for medical purposes are washed and sterilized frequently. For that reason, the optical symbols are directly formed (i.e., directly marked, or formed by direct part marking) typically on the surfaces of the steel instruments by such techniques as stamping and etching.
The term “optical symbol” is a generic term for an information medium that stores information by combinations of high optical reflectivity portions and low optical reflectivity portions. One example is a two-dimensional symbol (also referred to as a two-dimensional code or a two-dimensional barcode) in which information units referred to as cells are lined up vertically and horizontally. Specific examples include a QR code (tradename), a data matrix, and a data tag. The information of the two-dimensional symbols is read by a reading apparatus. The reading apparatus acquires image data of a two-dimensional symbol by illuminating the surface marked with the two-dimensional symbol with an illumination, such as a red LED (light emitting diode), and receiving the reflected light therefrom. The reading apparatus analyzes the image data and obtains the information recorded in the two-dimensional symbol.
However, in the case that the two-dimensional symbol is directly marked on the surface of a steel instrument, it may be more difficult to read the information than, for example, in the case that the two-dimensional symbol is printed on a label that is affixed to a steel instrument. For example, when the two-dimensional symbol is formed on a curved surface of the steel instrument, the illuminating light may undergo diffused reflection so that the reading apparatus cannot receive the reflected light. Alternatively, the illumination light may reflect on the surface of the steel instrument, causing halation, so that the acquired image data become completely white. Furthermore, accuracy variations in the direct part marking and deterioration resulting from long-term use may cause variations in the two-dimensional symbols. As a consequence, the reading apparatus may not be able to read the information of the two-dimensional symbols satisfactorily.
The technique disclosed in JP 2013-080515 A is known as a technique that solves this problem. JP 2013-080515 A discloses a two-dimensional symbol reading apparatus provided with a high-angle bright field illumination (for example, a red LED) and a low-angle dark field illumination (for example, a blue LED). The reading apparatus of JP 2013-080515 A adjusts illumination by combining two types of light sources having different angles of incidence, to read two-dimensional symbols formed on surfaces of objects with various shapes.
The apparatus disclosed in JP 2013-080515 A requires adjustment of the illuminations, for example, each time the type or surface shape of the steel instrument marked with a two-dimensional symbol changes. However, in a surgical operation, for example, a large number of steel instruments are used at one time. Also, a variety of steel instruments are used. This means that the user needs to carry out troublesome adjusting work of the illuminations repeatedly, resulting in low work efficiency and placing a heavy burden on the user.